I run my own DNS servers and Mail server, I have purchased a few battery backups that are available, they work but they only work for a limited time. With one backup per computer, which I have 3, they will run for about 45 minutes if the power goes out. None of them work properly with Windows Server 19 to shut down system then restart when the power comes back on. I have had to make multiple emergency trips to my home in Arizona where they are setup, just to turn them back on. Yes it sucks.
Can Linux be configured to shutdown properly with the backups you have? If yes, virtualize the Server 2019 machines under Proxmox.
Restart after power loss is, at least in the Dell servers I'm most familiar with, a setting in BIOS.